This invention relates to an astern-ahead switching device for a marine propulsion unit and more particularly to an improved shifting control for such a unit.
In marine propulsion transmissions, it is a normal practice to employ a bevel gear transmission comprised of a driving bevel gear and a pair of counterrotating driven bevel gears for selectively driving a propeller shaft in forward or reverse directions. Some form of shift mechanism is employed for moving a dog clutching element, which is positioned between the driven bevel gears, into selected engagement with either of the bevel gears for either forward or reverse drive.
In many applications, it is desirable to employ a pair of outboard drives for propelling a watercraft. However, in the use of such dual outboard drives, it is the normal practice to have the propeller shafts of the individual units rotate in opposite directions so as to reduce transverse thrust acting on the watercraft. This has previously been accomplished by providing units in which the engines drive in opposite directions. As a result, the right and left hand units of the prior art constructions have been substantially different and not fully interchangeable.
In U.S. Pat. No. 4,637,802, entitled "Twin Outboard Drive For Watercraft", issued Jan. 20, 1987, in the name of Michihiro Taguchi et al, and assigned to the assignee thereof, there is disclosed an arrangement wherein such a twin outboard drive can be employed without requiring oppositely rotating powering engines. In accordance with the construction shown in that patent, the shift mechanism is arranged so that when the shift levers controlling the two units are both moved in the forward direction, the bevel gear of one unit is moved in an opposite sense to the other unit. As a result, the reverse drive is possible without necessitating reversal of the direction of engine rotation.
In the embodiments shown in that application this reversal can be achieved by repositioning of certain components of the shift actuating mechanism. Although this provides simplicity and operation, certain elements of the shift actuating mechanism must be particularly designed for either the right or left hand side unit and are not interchangeable. This can give rise to a number of problems.
It is, therefore, a principal object of this invention to provide an improved shift actuating mechanism which permits selective reversal of the movement of the shifting member through repositioning of certain shift components without requiring different components to be substituted in order to reverse the direction of movement.
It is a further object of this invention to provide an improved shift actuating mechanism wherein the direction of shifting movement can be easily reversed merely by repositioning certain components.
It is a further object of this invention to provide an improved shift actuating mechanism wherein reversal can be achieved through the use of the same components but oriented in a different relationship.